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Systems & Data Center · Foundational

Linux Signals

Software interrupts sent to processes to request actions such as terminate, reload or stop, using commands like kill.

Definition

Common signals include SIGHUP (1, hang up or reload config), SIGINT (2, Ctrl+C), SIGKILL (9, forced termination that cannot be caught), SIGTERM (15, graceful default) and SIGSTOP (19, pause). kill, pkill and killall send them.

Example

kill -HUP $(pidof rsyslogd) asks rsyslog to reload; kill -9 1234 forcibly ends PID 1234.

Exam tip

Default kill sends SIGTERM (15); use SIGKILL (9) only when graceful termination fails.

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